Every enterprise I have worked at had both linux and mac available to developers. Is this not your experience? You seem to present as truth the opposite of what I have lived.
Counter-anecdote: every place I worked at including 4-5 major companies in various industries had compulsory windows desktops for everyone. The few of us that also had a Linux (or AIX/HP-UX/...) machines that we did our work on, SSHd into those machines.
Macs are usually only available to upper management, unless required for iOS development, in which case they are part of a pool shared among project teams.
Not at all. Linux can sometimes be made available on servers if necessary, but if you want Linux on your desktop you have to use a VM (ideally without telling IT). Never worked at a large place where Macs where readily available. Macs used to be more popular ~10 years ago or so with the marketing and communications people doing a lot of DTP and design work, but even that seems to have greatly decreased.
And don’t forget that developers are a tiny minority of employees.
However i work with Rails, Python and fancy things. I know if i would look into .NET/suit wearing side of things, things would look very different.